1. Field of the Invention
The present invention relates to a control technique of shake compensation configured to prevent image deterioration by compensating for image shake caused by vibration resulting from camera shake, or the like.
2. Description of the Related Art
A camera is commercially available that includes a shake compensation control apparatus including a shake compensation unit, drive unit, vibration detection unit, and the like configured to prevent image shake due to camera shake or the like and thereby reduce factors that result in an imaging error by a photographer.
In this context, a shake compensation control apparatus will be briefly described. To enable performance of imaging without image shake even when camera shake occurs during the imaging operation, shaking of the camera resulting from camera shake is detected and displacement control of an image shake compensation lens (hereinafter referred to as a “shake compensation lens (image blur correction lens)”) or imaging element is executed in response to a detection value. That process requires accurate detection of camera vibration and compensation of variation in the optical axis due to shaking. In principle, vibration detection is executed by the vibration detection unit calculating a detection result such as a rotational velocity or the like. Image shake can be suppressed by controlling a vibration detection unit based on the calculation processing result to thereby displace the shake compensation lens (image blur correction lens) or the imaging element.
A variety of optical devices include an apparatus that is configured to detect rotational shake using a rotational velocity meter and drive an imaging lens or imaging element to thereby reduce image shake. However, when imaging at a close range (imaging conditions associated with a high imaging magnification), vibration occurs that cannot be detected only by use of a rotational velocity meter. For example, it is not possible to ignore image deterioration caused by vibration resulting from shake that is applied in a horizontal or vertical direction in a plane that is orthogonal to the optical axis of the camera, in other words, so-called translational shake. For example, macro-imaging by approaching to about 20 cm of the object to be imaged requires active detection and compensation of translational shake. It is also necessary to detect and compensate for translational shake during imaging under conditions when the focal distance of the imaging optical system is extremely large (for example, 400 mm) even when the object to be imaged is positioned at a distance of approximately one meter from the camera.
The technique disclosed in Japanese Patent Application Laid-Open No. 7-225405 is configured to calculate translational shake by application of double integration to the acceleration detected by an acceleration meter and thereby drive a shake compensation unit by including the output of a separately provided rotational velocity meter. However, the output of the acceleration meter used in the detection of translational shake exhibits a tendency to be affected by environmental fluctuation such as disturbances, noise or temperature change. Consequently, high accuracy compensation of translational shake is difficult since the effect of these unstable factors is further increased by double integration of the detected acceleration.
Japanese Patent Application Laid-Open No. 2010-25962 discloses calculation of translational shake by treating translational shake as rotational shaking when there is a center of rotation at a position separated from the camera. This method executes shake compensation by providing a rotational velocity meter and an acceleration meter and using the output of those meters to calculate a compensation value and an angle using a rotation radius of the rotational shake. A reduction in accuracy resulting from unstable factors caused by an acceleration meter as described above can be mitigated by calculation of a rotation center and limiting to frequency bands in which the effect of disturbances is low.
In a conventional technique, compensation of translational shake is associated with the following conditions. Although it is preferred that the mounting position for the acceleration meter is the lens principal point in a method using an acceleration meter in a detection unit for executing compensation of translational shake, it is difficult to provide an acceleration meter in proximity to the lens principal point.
Japanese Patent Application Laid-Open No. 2010-25962 discloses a method of detecting shake using the output of an imaging unit in substitution for an acceleration meter as a shake detection unit. When shake is detected using the output of an imaging unit, a method may be used in which a compensation coefficient (correction coefficient) is calculated from the relationship between the image shake and the rotational shake immediately prior to the imaging operation, and the compensation is applied to rotational shake during the imaging operation. In this case, translational shake compensation is only not performed during the imaging operation.
Japanese Patent Application Laid-Open No. 2010-25962 also discloses a method of detecting acceleration of translational shake from the current that flows in the driving coils in substitution for an acceleration meter as a shake detection unit. However, this method does not enable performance of shake compensation unit immediately prior to the imaging operation.
The present invention has the object of improving operational characteristics with a downsized configuration and executing high accuracy image shake compensation in relation to translational shake without reference to a change in a focal distance or a shake compensation range.